If you want to convert a class file into a readable source code, you can try to use the Jad (JAva Decompiler). It is free for download and easy to use. You can refer to this url for further information about jad: http://www.kpdus.com/jad.html

Here are the steps to decompile a class file using Jad:-

1. Access to the directory where jadnt (jad) has been installed. (Please ensure that the jad.exe is inside the folder)
2. Copy the single .class file into the directory.
3. Open Windows command prompt.
4. Type the location of the directory in the command prompt. (e.g. C:/jadnt158)
5. Type jad .class
6. In the directory, open the file with the .jad using vi editor or Notepad